PleasantSt256-NOI-StormwaterRptAppendix I
Stormwater Report – Review of Stormwater Standards
Summary of the Work. Part of the Market Street Brook drain system will be relocated. The existing drain to be relocated consists approximately 305-LF of 60” by 68” brick arched drain
[full capacity = 266.9 CFS]. The proposed relocated drain will about 330-LF of 72” by 72” box drain. The relocated drain will have slightly higher capacity than the existing drain.
The entire area of the proposed relocation work is currently impervious; paved parking area and roadway. The proposed relocation, when completed will replace the disturbed impervious
surfaces. As such, the project qualifies as redevelopment, see Standard 7 below.
The proposed development of this site attempts to satisfy the MA Stormwater Management Standards to the maximum extent practicable. The MA Stormwater standards are summarized below:
No new stormwater conveyances may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. The existing drain (to be abandoned) has seven
(7) stormwater connections. These connections include: two (2) direct discharges from catch basins in the parking lot (located directly over the drain); four (4) piped connections
from additional catch basins in the parking lot; and one piped connection from a roadway drainage system located in Holyoke Street. This project will eliminate the two directly connected
catch basins and reduce the remaining connections to two (2) piped connections: one in the parking lot and one from Holyoke Street. These are historic drainage connections to this
resource.
Treatment is provided by street sweeping and catch basin maintenance (one to two times per year) and replacing two catch basins in Holyoke Street with deep sump hooded catch basins (DSHCBs).
No additional treatment is proposed (as part of this project) for the catch basins located within the parking lot.
The currently proposed site development [not included as part of this permit] is planned to include: (a) conversion of some impervious surfaces to vegetated surfaces (>11,000-SF); (b)
installation of a rain garden; and (c) installation of a proprietary stormwater treatment system (Stormceptor). These proposed site modifications have been permitted in accordance
with the Northampton stormwater regulations. Please note that there is no guarantee that the proposed site development will proceed as planned and should not be considered as a condition
of this permit.
Based on the above, the City has met this standard to the maximum extent practicable.
Post-development peak discharges shall not exceed pre-development peak discharge rates. The existing site is covered with impervious surface. The proposed drain relocation will not
increase the amount of impervious surface and will not increase the peak runoff flows from this site. In addition, the proposed drain has been designed to similar hydraulic characteristics
as the existing drain; i.e. the proposed work should not increase flow or flooding to downstream receptors.
Based on the above, the City has met this standard to the maximum extent practicable.
The annual recharge from post-development site shall approximate the annual recharge from pre-development conditions based on soil conditions. The proposed project is redevelopment
and is not anticipated to have an impact on site recharge. Allowing this proposed drain relocation provides an opportunity for a separate project that may increase infiltration. )
This standard is met to the extent practicable for this site.
The stormwater system shall remove 80% of the annual average post construction load of Total Suspended Solids (TSS). This standard is met when:
Suitable practices for source control and pollution prevention are identified in a long-term pollution prevention plan, and thereafter implemented and maintained;
Structural stormwater best management practices (BMPs) are sized to capture the required water quality volume determined in accordance with the MA Stormwater Handbook; and
Pretreatment is provided in accordance with the MA Stormwater Handbook
The City proposes to conduct street sweeping and catch basin maintenance one to two times per year. It is also the City’s policy to replace existing catch basins with deep sump hooded
catch basins (DSHCBs) where feasible. This practice does not meet the 80% TSS removal goal, but is considered reasonable due to the limited area within city streets for installing
treatment devices.
This standard is met to the extent practicable for this site, based on site constraints.
For land uses with higher potential pollutant loads (LUHPPL), source control shall be implemented in accordance with the MA Stormwater Handbook to eliminate or reduce the discharge of
stormwater runoff from such land uses to the maximum extent practicable; these discharges shall also comply with the requirements of the MA Clean Waters Act (MGL c21 s26-53) as regulated
by 314 CMR 3.00, 314 CMR 4.00 and 314 CMR 5.00.
This site is not a LUHPPL. This standard is generally not applicable to this site.
Stormwater discharges within Zone II or Interim Wellhead Protection Area (IWPA) and stormwater discharges near or to any other critical area, require the use of specific source control
and pollution prevention measures and the specific structural stormwater BMPs determined to be suitable for such uses as provided in the MA Stormwater Handbook.
This standard is not applicable to this site.
A redevelopment project is required to meet the MA Stormwater Management Standards 2, 3, 4, 5 & 6 only to the maximum extent practicable; and is also required to meet other standards
and improve existing conditions.
This standard does apply as this is a re-development site as discussed above.
A Construction period Erosion, Sedimentation and Pollution Prevention Plan shall be developed and implemented. This plan is provided with this Notice of Intent, see proposed site plans
and Appendix F of the NOI.
A long term Operation & Maintenance Plan shall be developed and implemented. The long term operation and maintenance plan for the proposed drain includes: street sweeping; catch basin
maintenance cleaning (1 to 2 times per year); regular inspection of the drain; and cleaning/maintenance of the drain as required based on inspection or other reported events.
All illicit discharges to the stormwater management system are prohibited. This standard will apply to this site. See attached “Illicit Discharge Compliance Statement”. This standard
will be met by requiring each contractor working on the site to provide an Illicit Discharge Compliance Statement.